Turbine blades of a gas turbine are exposed to a high-temperature, high-pressure working fluid and thus have internal cooling structures. Specifically, the turbine blades each have, for example, a flow channel inside as a cooling structure, and compressed air extracted from a compressor flows in the flow channel as cooling air, thereby internally cooling the turbine blade. A turbine blade on the front stage side of the gas turbine and a turbine blade on the rear stage side have mutually different lengths and the like, and the working fluid flows around these turbine blades at mutually different temperatures. Thus, these turbine blades have mutually different cooling conditions. This means that the internal cooling flow channels are required to have different structures between the turbine blades on the front stage side and the rear stage side.
Patent Document 1 discloses an example of the cooling structure on the rear stage side. Specifically, in a turbine blade disclosed in Patent Document 1, a cavity in which pin fins project from the inner wall is provided inside a hub and a blade root, and multi-holes that communicate with the cavity and an opening formed in a blade tip and through which cooling air passes from the cavity to the opening are formed inside the blade on the blade tip side with respect to the hub.